1. Field of the Invention
The present invention relates to transducers and, more specifically, to transducers having variable resonance.
2. Description of the Prior Art
In order to produce high amplitude low frequency signals, underwater transducers must generate a relatively large volume displacement. Since water exerts a large reaction force back on the transducer, conventional wisdom dictates that such a transducer would have to be a high Q resonant device and thus not be broad band. However, a transducer does not have to be broad band in the conventional sense to meet the requirements of communication and SONAR systems. A transducer that is capable of switching between two discrete frequencies is adequate for many communication applications and one that is capable of switching among several frequencies could produce the chirp signals and codes commonly used in active sonars and oceanographic and geophysical research. Ordinarily, a broad band transducer is needed to accomplish the frequency switching rapidly.
No device or method exists which switches frequency in a transducer without having to add substantial amounts of energy to the system.